VIT Engineering VIT Engineering Solved Paper-2008

  • question_answer
    If x, y, z are different from zero and\[\Delta =\left| \begin{matrix}    a & b-y & c-z  \\    a-x & b & c-z  \\    a-x & b-y & c  \\ \end{matrix} \right|=0,\] then the value of the expression \[\frac{a}{x}+\frac{b}{y}+\frac{c}{z}\] is

    A)  0             

    B)  -1

    C)  1              

    D)  2

    Correct Answer: D

    Solution :

    \[\left| \begin{matrix}    a & b-y & c-z  \\    a-x & b & c-z  \\    a-x & b-y & c  \\ \end{matrix} \right|=0\] \[\Rightarrow \]\[a\left| \begin{matrix}    b & c-z  \\    b-y & c  \\ \end{matrix} \right|-(b-y)\left| \begin{matrix}    a-x & c-z  \\    a-x & c  \\ \end{matrix} \right|\] \[+(c-z)\left| \begin{matrix}    a-x & b  \\    a-x & b-y  \\ \end{matrix} \right|=0\] \[\Rightarrow \]\[a(bc-bc+bz+cy-yz)-(b-y)\] \[\left( ac-cx-ac+az+cx-xz \right)+\left( c-z \right)\] \[\left( ab-ay-bx+xy-ab+bx \right)=0\] \[\Rightarrow \]\[a(bz+cy-yz)-(b-y)(az-zx)+(c-z)\] \[(xy-ay)=0\] \[\Rightarrow \]\[abz+acy-ayz-abz+bxz+ayz-xyz\] \[+cxy-acy-xyz+ayz=0\] \[\Rightarrow \]\[ayz+bxz-2xyz+cxy=0\] \[\Rightarrow \]\[ayz+bxz+cxy=2xyz\] \[\Rightarrow \]\[\frac{ayz}{xyz}+\frac{bxz}{xyz}+\frac{cxy}{xyz}=2\] \[\Rightarrow \]\[\frac{a}{x}+\frac{b}{y}+\frac{c}{z}=2\]


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